Energy deposition in small cylindrical targets by monoenergetic electrons.

Calculations of energy deposition in cylindrical target volumes of diameter and height 1-100 nm, including those similar to the dimensions of biological molecules and structures such as DNA, nucleosomes and chromatin fibre, have been made. The calculations used the Monte Carlo track structure program MOCA8B for electrons of initial energy 0.1-100 keV. Details of the calculation are presented, as well as a selection of results. The frequency distributions of energy deposition events per gray per target, placed at random in a homogeneous aqueous medium, are given for uniform irradiation with monoenergetic electrons of various energies. The frequency distributions have been used to predict the initial biophysical parameters such as relative effectiveness for initial damage. These suggest that the final biological effects which depend on complex local damage may show substantial variations in biological effectiveness for different low linear energy transfer radiations, whereas those that depend on simple local damage may not.